Method of fabricating light-emitting diode with a micro-structure lens

ABSTRACT

A light emitting diode (LED) with a micro-structure lens includes a LED die and a micro-structure lens. The micro-structure lens includes a convex lens portion, at least one concentric ridge structure surrounding the convex lens portion, and a lower portion below the convex lens portion and the at least one concentric ridge structure. The lower portion is arranged to be disposed over the LED die. A first optical path length from an edge of the LED die to a top center of the microstructure lens is substantially the same as a second optical path length from the edge of the LED die to a side of the micro-structure lens.

PRIORITY DATA

The present application is a divisional of U.S. patent application Ser.No. 13/087,564, filed on Apr. 15, 2011, now U.S. Pat. No. 8,969,894issued Mar. 3, 2015, the disclosure of which is hereby incorporated byreference in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to a light emitting diode (LED)and more particularly to a LED with a micro-structure lens.

BACKGROUND

For a primary LED lens design, light-extraction efficiency and spatialcolor shift characteristics are important factors. The primary LED lenswill affect secondary optical design and backend product applications. Aconventional dome lens may improve light extraction performance, but itwould have undesirable spatial color shift due to different optical pathlengths in different directions.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is now made to the following descriptions taken in conjunctionwith the accompanying drawings, in which:

FIG. 1 is a schematic diagram showing an exemplary LED with amicro-structure lens according to some embodiments;

FIG. 2A is a schematic diagram showing a side view of an exemplarymicro-structure lens for an LED according to some embodiments

FIG. 2B is a schematic diagram showing a top view of the exemplarymicro-structure lens for the LED in FIG. 2A;

FIG. 2C is a schematic diagram showing a three-dimensional view of theexemplary micro-structure lens for the LED in FIG. 2A;

FIG. 3A is a schematic diagram showing a side view of another exemplarymicro-structure lens for an LED according to some embodiments;

FIG. 3B is a schematic diagram showing a top view of the exemplarymicro-structure lens for the LED in FIG. 3A;

FIG. 3C is a schematic diagram showing a three-dimensional view of theexemplary micro-structure lens for the LED in FIG. 3A;

FIG. 4A is a schematic diagram showing a side view of yet anotherexemplary micro-structure lens for an LED according to some embodiments;

FIG. 4B is a schematic diagram showing a top view of the exemplarymicro-structure lens for the LED in FIG. 4A;

FIG. 4C is a schematic diagram showing a three-dimensional view of theexemplary micro-structure lens for the LED in FIG. 4A;

FIG. 5 is a plot showing Y/B ratio of various LEDs according to someembodiments; and

FIG. 6 is a flowchart of a method for fabricating the exemplary LED witha micro-structure lens in FIG. 1 according to some embodiments.

DETAILED DESCRIPTION

The making and using of various embodiments are discussed in detailbelow. It should be appreciated, however, that the present disclosureprovides many applicable inventive concepts that can be embodied in awide variety of specific contexts. The specific embodiments discussedare merely illustrative of specific ways to make and use, and do notlimit the scope of the disclosure.

FIG. 1 is a schematic diagram showing an exemplary LED with amicro-structure lens according to some embodiments. An LED assembly 100includes a substrate 102 and an LED die 108. A reflective layer 104,e.g., silver (Ag), is formed on the substrate 102, e.g., silicon (Si).The LED die 108 is mounted on the substrate 102, e.g., by bonding usinga solder layer 106. The size of the LED die 108 varies depending onapplications, e.g., 300 μm-2000 μm. For low power applications, the LEDdie 108 may have a size of 300 μm-600 μm; while for high powerapplications, the LED die 108 may have a size of about 1000 μm or more.

A phosphor coating 110 is deposited over the LED die 108 to form adesired light color from the LED assembly 100. For example, the color oflight emitted by the LED die 108, e.g., made of InGaN, may be blue, anda yellow phosphor material, e.g., cerium-doped yttrium aluminum garnet(Ce³⁺XAG), can be used to form a white light. Also, depending on thespecific material and the thickness of the phosphor coating 110, e.g.,30 μm-60 μm, the light color can be changed. The phosphor coating 110can use various materials, which are known in the art. The phosphorparticle size can range, e.g., 6 μm-30 μm, in some embodiments. Thephosphor material can form a conformal coating on the LED die 108 bycontrolled dispensing of the phosphor, e.g., spraying.

A micro-structure lens 114, including a micro-structure 116 on top and alower portion 122, is molded over the substrate 102 and the LED die 108,which also forms a lens base layer 112 at the same time. The size of themicro-structure lens 114 varies depending on applications, and itsdiameter can be about 2.5 times of the size of the LED die 108. Themicro-structure lens 114 and the lens base layer 112 can comprisesilicon (Si), for example. The micro-structure 116 includes at least oneconcentric ridge structures 120 in addition to a convex lens portion118. The micro-structure 116 can have a similar structure as a Fresnellens structure, but not limited to it. Different structures are shownbelow in FIGS. 2A-4A. The lower portion 122 is shaped to enhance lightextraction efficiency, e.g., as a part of a dome lens, where the toppart of the dome lens is replaced by the micro-structure 116.

In general, the reflection at the surface of an LED lens is reduced byusing a dome-shaped (half-sphere or hemisphere) package with the LED atthe center so that the outgoing light rays strike the surfaceperpendicularly, at which angle the reflection is minimized. Thereflective layer 104 on the substrate 102 increases the LED efficiency.The refractive index of the package material can also match therefractive index of the LED (semiconductor), to minimizeback-reflection. An anti-reflection coating may be added as well.

The micro-structure lens 114 is designed to make optical path length(OPL) between the LED die 108 and the lens surface uniform as much aspossible, thus improving the spatial color uniformity and still havehigh light extraction efficiency from the LED assembly 100. For example,a first length OPL1 from an edge of the LED die 108 to the top center ofthe micro-structure lens 114 (or the convex lens portion 118) and asecond length OPL2 from the edge of the LED die 108 to the side of themicro-structure lens 114 are substantially the same.

In comparison, a conventional dome lens would have a hemisphericalstructure and the same radius from the center of the hemisphere to thetop and a side of the dome lens. Because of the size of the LED die 108,the OPL from an edge of the LED die 108 to the top and a side of thedome lens would be substantially different. For example, the diameter ofthe conventional dome lens can be about 2.5 times of the length of theLED die 108. Assuming the length of the LED die 108 (positioned at thecenter of a hemispherical dome lens) is about 300 μm, the diameter ofthe dome lens can he about 750 μm, and the difference of OPL can be morethan 100 μm, Due to the large difference in OPL, a significant specialcolor shift will result for the conventional dome lens, e.g., a yellowring at the edge of a white light LED.

In one exemplary design for the micro-structure lens 114, a dome typelens is designed first, using an optical design software. The lens shapeis hemispherical to enhance the light extraction efficiency of the LEDassembly 100. Then the height of the dome lens can be reduced. by usinga micro-structure 116. The optical design software can be used tooptimize the lens structure performance (e.g., high light extractionefficiency and enhanced color uniformity).

For the fabrication of the LED assembly 100, a substrate (e.g., Si) 102is provided, and a reflective layer 104 is formed on the substrate 102.A bare LED die 108 is bonded on a substrate 102, e.g., using a solderlayer 106 that is disposed over the reflective layer 104. A conformalphosphor coating 110 is formed. The phosphor coating 110 has arelatively small particle size, e.g., 6 μm-30 μm, forming a thinphosphor layer, e.g., 30 μm-60 μm, in some embodiments.

For the fabrication of micro-structure lens 114, the lens shape ismolded using a lens molding instrument. A lens molding process is knownin the art. If the details of the micro-structure lens 114, e.g., theridge structures 120, are not well defined with precision, a dry/wetetching process can be used to obtain better defined structures aftermolding. The ridge structures 120 have a height/depth of about 3 μm-5 μmin some embodiments.

FIG. 2A is a schematic diagram showing a side view of an exemplarymicro-structure lens 114 for an LED according to some embodiments. Themicro-structure lens 114 has three concentric ridge structures 120 and aconvex lens portion 118 on top in FIG. 2A. The three concentric ridgestructures 120 have pointed peaks, similar to a Fresnel lens structure.As mentioned above, if the details of the micro-structure lens 114,e.g., the ridge structures 120, are not well defined with precisionafter the lens molding, a dry/wet etching process can be used to obtainbetter defined structures. FIG. 2B is a schematic diagram showing a topview of the exemplary micro-structure lens 114 for the LED in FIG. 2A.FIG. 2C is a schematic diagram showing a three-dimensional view of theexemplary micro-structure lens 114 for the LED in FIG. 2A.

FIG. 3A is a schematic diagram showing a side view of another exemplarymicro-structure lens 114 for an LED according to some embodiments.Compared to the exemplary micro-structure lens in FIG. 2A, the top ofthe concentric ridge structures 120 are not pointed, but rather curvedin FIG. 3A. The height of the concentric ridge structures 120 are thesame as each other, but he top of the convex lens portion 118 is higherthan the top of the ridge structures 120. The different lens designs areselected for different implementations and applications, based onperformances (simulated or experimental), and ease of fabrication, etc.FIG. 3B is a schematic diagram showing a top view of the exemplarymicro-structure lens 114 for the LED in FIG. 3A. FIG. 3C is a schematicdiagram showing a three-dimensional view of the exemplarymicro-structure lens 114 for the LED in FIG. 3A.

FIG. 4A is a schematic diagram showing a side view of yet anotherexemplary micro-structure lens 114 for an LED according to someembodiments. The top of the concentric ridge structures 120 are circularinstead of triangular, and the height of the concentric ridge structures120 are different from each other in FIG. 4A. The diameter and height ofthe concentric ridge structures 120 increase as they get closer to thecenter of the micro-structure lens 114. The top of the convex lensportion 118 is higher than the top of the ridge structures 120. FIG. 4Bis a schematic diagram showing a top view of the exemplarymicro-structure lens 114 for the LED in FIG. 4A. FIG. 4C is a schematicdiagram showing a three-dimensional view of the exemplarymicro-structure lens 114 for the LED in FIG. 4A.

FIG. 5 is a plot showing a yellow/blue (Y/B) ratio of various LEDsaccording to some embodiments. A Y/B ratio plot 502 of an LED withoutany lens shows a very low value (predominantly blue) at the center (lowview angle), and increases (predominantly yellow) to either side edges(high view angles on either side). The Y/B ratio varies from about 0.13to about 0.75. A Y/B ratio plot 504 of an LED with a conventional lensshows similar trends, and the Y/B ratio varies from about 0.23 to about0.58. Compared to those two plots, a Y/B ratio plot 506 of an LED withan exemplary micro-structure lens 114 shows improved color distributionuniformity. The WB ratio varies from about 0.38 to about 0.53 in thisexample.

FIG. 6 is a flowchart of a method for fabricating the exemplary LED witha micro-structure lens in FIG. 1 according to some embodiments. At step602, a light emitting diode (LED) die on a substrate is provided. Atstep 604, the micro-structure lens that has at least one concentricridge is molded over the LED die. A first optical path length from anedge of the LED die to a top center of the micro-structure lens issubstantially the same as a second optical path length from the edge ofthe LED die to a side of the micro-structure lens.

In various embodiments, a reflective layer is formed on the substrate. Asolder layer is formed on the reflective layer. The LED die is bonded tothe substrate. The LED die is wire bonded. A phosphor coating is formedon the LED die. The micro-structure lens is etched after molding.

According to some embodiments, a light emitting diode (LED) with amicro-structure lens includes a LED die and a micro-structure lens. Themicro-structure lens includes a convex lens portion, at least oneconcentric ridge structure surrounding the convex lens portion, and alower portion below the convex lens portion and the at least oneconcentric ridge structure. The lower portion is arranged to be disposedover the LED die. A first optical path length from an edge of the LEDdie to a top center of the micro-structure lens is substantially thesame as a second optical path length from the edge of the LED die to aside of the micro-structure lens.

According to some embodiments, a method of fabricating a light emittingdiode (LED) with a micro-structure lens includes providing a lightemitting diode (LED) die on a substrate. The micro-structure lens ismolded that has at least one concentric, ridge over the LED die. A firstoptical path length from an edge of the LED die to a top center of themicro-structure lens is substantially the same as a second optical pathlength from the edge of the LED die to a side of the micro-structurelens.

A skilled person in the art will appreciate that there can be manyembodiment variations of this disclosure. Although the embodiments andtheir features have been described in detail, it should be understoodthat various changes, substitutions and alterations can be made hereinwithout departing from the spirit and scope of the embodiments.Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, and composition of matter, means, methods and stepsdescribed in the specification. As one of ordinary skill in the art willreadily appreciate from the disclosed. embodiments, processes, machines,manufacture, compositions of matter, means, methods, or steps, presentlyexisting or later to be developed, that perform substantially the samefunction or achieve substantially the same result as the correspondingembodiments described herein may be utilized according to the presentdisclosure.

The above method embodiment shows exemplary steps, but they are notnecessarily required to be performed in the order shown. Steps may beadded, replaced, changed order, and/or eliminated as appropriate, inaccordance with the spirit and scope of embodiment of the disclosure.Embodiments that combine different claims and/or different embodimentsare within the scope of the disclosure and will be apparent to thoseskilled in the art after reviewing this disclosure.

What is claimed is:
 1. A method of fabricating a light emitting diode(LED) with a micro-structure lens, comprising: receiving a lightemitting diode (LED) die on a substrate; and molding the micro-structurelens that has at least one concentric ridge over the LED die, wherein afirst optical path length from an edge of the LED die to a top center ofthe micro-structure lens is substantially the same as a second opticalpath length from the edge of the LED die to a side of themicro-structure lens.
 2. The method of claim 1, further comprisingforming a reflective layer on the substrate.
 3. The method of claim 2,further comprising forming a solder layer on the reflective layer. 4.The method of claim 1, further comprising bonding the LED die to thesubstrate.
 5. The method of claim 1, further comprising wire bonding theLED die.
 6. The method of claim 1, further comprising forming a phosphorcoating on the LED die.
 7. The method of claim 1, further comprisingetching the micro-structure lens after the molding.
 8. A method,comprising: forming a reflective layer over a substrate; bonding alight-emitting diode (LED) die to the reflective layer; coating aphosphor material over the LED die; and molding a lens over the LED diesuch that the lens is molded to have a convex lens portion and aplurality of ridges circumferentially surrounding the convex lensportion in a top view, wherein a first optical path length from an edgeof the LED die to a top center of the lens is about the same as a secondoptical path length from an edge of the LED die to a side of the lens,and wherein the convex lens portion has a greater lateral dimension thanthe LED die.
 9. The method of claim 8, wherein the molding of the lenscomprises molding a curved side surface of the lens and molding pointedor curved peaks for the plurality of ridges, respectively.